How to Be Anything – Episode 6: How to Search for Dark Matter Underground and in Space

Podcast: How to Be Anything
Host: Emily McCrary (Anything & Everything Podcasts)
Original Release: August 13, 2025

Episode Overview

This episode dives into the mysterious world of dark matter and profiles the people who dedicate their careers to searching for it—both miles underground and far out in space. Host Emily McCrary introduces physicist Dan Hooper (University of Wisconsin, director of the Wisconsin IceCube Particle Astrophysics Center) and Gavin Cox (experiment support scientist at the Sanford Underground Research Facility), who explain how we know dark matter exists, the ingenious ways we try to detect it, and what it might mean for the future of science if we finally find it. The episode blends accessible analogies, vivid storytelling, and personal accounts of unconventional scientific careers.

Key Discussion Points & Insights

1. What is Dark Matter? The Mystery Defined

[00:47–02:25]

• Most of the universe’s matter is invisible—85% is “dark matter,” which we can't see or directly detect, but infer from its gravitational effects.

  • Dan Hooper: “We know that most of the matter in our universe is not made of atoms or really of anything else that appreciably radiates, reflects, or absorbs light. So we can't see it. But we're pretty sure...it's there because of all the ways we feel its gravity.” [01:10]

• Analogy: Dark matter is like something causing cars to swerve, even though you can’t see the object itself—its presence is only known by indirect effects.

  • Emily McCrary: “That's how we know dark matter is there, even if we haven't definitively detected it...” [02:25]

2. A Brief History of Dark Matter Science

[03:38–05:31]

• The idea is less than 100 years old, with early hints from the work of Fritz Zwicky in the 1930s and later observations by Vera Rubin and others.

  • Dan Hooper: “He noticed...the galaxies in the system we call the Coma Cluster...were all moving really fast, much faster than we could explain with the gravity of the normal matter...” [03:38]

• Over decades, scientists eliminated alternative explanations (e.g., faint stars, black holes)—suggesting dark matter is a new, unseen form of matter.

3. What Do We Actually Know About Dark Matter?

[05:33–06:19]

• We know the amount, “it’s not moving very fast,” and it’s stable, inert, and invisible.
  • Dan Hooper: “It’s some sort of stable, very inert, very invisible form of matter that isn’t moving very quick...And that’s about it.” [05:33]

4. How Do We Search for Dark Matter? Going Underground

[06:27–12:09]

• Deep Underground Detectors:
  Since the 1980s, physicists seek to directly detect dark matter—often “WIMPs” (weakly interacting massive particles)—by building massively sensitive detectors deep underground to shield from cosmic noise.

  • Detectors have gone from “something you could hold in your hand” to “tens of tons of detector mass...millions or maybe billions of times as sensitive.” Dan Hooper [06:27]

• Profile: Gavin Cox and the LZ Detector

  • Gavin Cox: “My name is Gavin Cox, and I’m an experiment support scientist at the Sanford Underground Research Facility in Leeds, South Dakota.” [07:33]
  • The LZ detector is a two-meter titanium cylinder holding nearly 10 tons of liquid xenon, isolated in a decommissioned gold mine a mile underground.
    • Gavin Cox: “We’re looking for one very specific type [of dark matter]...a WIMP...” [08:33]

• How It Works:

  • Xenon tank detects rare particle interactions: A passing WIMP might hit a xenon nucleus, producing a flash of light and a release of electrons.
    • Gavin Cox: “Depending on how much light and how many electrons are released during this interaction, we’ll be able to say whether it is or is not a dark matter interaction.” [09:27]

• The Underground Life:

  • Four days a week in the lab below ground, monitoring thousands of instruments.
    • Gavin Cox: “There’s an incredible amount of instruments inside this detector. It’s in the thousands, maybe up to 10,000.” [11:12]
  • On the quirks of the job:
    • Gavin Cox: “I remember getting on the cage for the first time six years ago and being very aware that I was standing over a mile deep hole...That was definitely scary at first...now it just turns into a commute.” [12:09]

5. Searches in Space: The Fermi Telescope and the Gamma-Ray Bump

[13:37–22:35]

• Space-Based Searches:
  While underground searches look for one kind of interaction (WIMPs colliding with xenon), space telescopes (like the Fermi Gamma Ray Space Telescope) look for other signatures—such as particles produced by the collision or decay (“annihilation”) of dark matter in space.

  • Dan Hooper: “You could detect things like gamma rays or other energetic forms of ordinary matter. If those sort of interactions are going on in our galaxy...” [15:28]

• The Axion Alternative:
  Another dark matter candidate, axions, which are light particles that interact with magnetic fields—a different focus from WIMPs.

• The Fermi Bump Discovery:

  • NASA’s Fermi Telescope (launched 2008) mapped gamma rays from the Milky Way’s center.
  • Dan Hooper and Lisa Goodenough analyzed early data, expecting to rule out dark matter models, but instead found an unexplained “bump” in the gamma-ray spectrum.
    • Dan Hooper: “There was this big bump in the spectrum, looked just like the bump you’d expect from dark matter...kind of had all the features you’d expect...” [18:25]
  • Hooper’s team’s claims endured skepticism and initial rejection—'you must be doing something wrong,' reviewers said. Only after accumulating more data and teaming with other researchers did NASA acknowledge the signal.
    • Dan Hooper: “We just couldn’t get it through peer review...We kept being told Fermi would have told us already...I thought we must have screwed something up.” [20:36]
    • With more data and better analysis, NASA ultimately issued a press release in 2014 recognizing the signal's potential significance.
    • NASA (via Emily McCrary): “A new study of gamma ray light from the center of our galaxy makes the strongest case to date that some of this emission may arise from dark matter...” [21:56]

• What’s Next?

  • The community agrees the signal exists, but debates remain: Is it truly dark matter, or an undiscovered astrophysical phenomenon?

6. What Would It Mean to Find Dark Matter?

[22:57–25:24]

• Discovery could “blow the doors off” our current understanding, leading to new branches of science—just as discovering gases led to chemistry and new elementary particles enabled quantum mechanics.
  • Dan Hooper: “When we discover new forms of matter and energy, it tends to lead to things that we weren’t anticipating...I think there’s a good reason to think that if we learn what the dark matter is, how it interacts, we would be able to learn completely new things, new branches of physics that we currently don’t have access to.” [22:57]
  • Understanding dark matter’s formation could also let us probe the conditions of the universe mere fractions of a second after the Big Bang.

Notable Quotes & Memorable Moments

• On certainty and humility:
  • Dan Hooper: “The short answer is we don’t really know.” [01:10]
• On the size and challenge of modern experiments:
  • Dan Hooper: “Now we're talking about tens of tons of detector mass. We go, you know, miles underground and build these elaborate laboratories...they're millions or maybe billions of times as sensitive as those first dark matter detectors.” [06:27]
• On the initial fear of working a mile underground:
  • Gavin Cox: “...being very aware that I was standing over a mile deep hole and the only thing preventing me from dropping down was a couple inches of steel. That was definitely scary at first, but I've been doing it for so long that it just turns into a commute.” [12:09]
• On scientific null results:
  • Dan Hooper: “Even null results, even negative results teach us something about our universe. In this case, it teaches us what some of the things that dark matter cannot be.” [15:18]
• On the Fermi “bump” and surprising results:
  • Dan Hooper: “My first reaction wasn't dark matter. My first reaction is like, huh, what's that? ... None of those things made it go away.” [20:01]
• On the magnitude of future discovery:
  • Dan Hooper: “[Discovering dark matter] might allow us to look back farther in time than we've ever been able to look, understand the true, like, primordial conditions of our universe, infinitesimally close to the Big Bang. I, for one, am very excited to see that happen.” [25:24]

Timeline of Important Segments

| Timestamp | Segment Description | |:----------:|-----------------------------------------------------------------------------------| | 00:47–02:25| Introduction to dark matter and its indirect detection | | 03:38–05:31| Historical context—early evidence and ruling out alternatives | | 06:27–13:37| Methods of underground detection, LZ experiment, and Gavin Cox’s day-to-day work | | 13:37–15:28| Space-based searches and what scientists look for in cosmic data | | 16:20–22:35| The Fermi Gamma-Ray “bump,” the challenge of peer review, and scientific drama | | 22:57–25:24| Implications of a discovery—how dark matter could reshape science |

Episode Tone and Style

The episode is approachable, engaging, and laced with wonder—balancing layperson-friendly metaphors (traffic, coffee shop) with detailed accounts of scientific process and real-life anecdotes of scientists’ day jobs. Both guests and the host emphasize the humility, patience, and stubborn curiosity required to chase the invisible through career paths that few outside physics even know exist.

Final Thought

The episode ends on a playful note, with Prof. Hooper mentioning his “physics punk rock band,” illustrating just how eclectic and varied the professional lives in science can be.

Dan Hooper: “For the purposes of this podcast, I will point out my physics punk rock band, the Spectral Distortions...We have songs that are broadly themed around physics and physics culture, including many of our things that frustrate us about physics.” [25:57]

Recommended For:
Anyone fascinated by the mysteries of the universe, the practical realities of cutting-edge science, or the real lives of those dedicated to expanding the boundaries of human knowledge.